Not ascertained in 1960. In 1970, families and unrelated individuals (excluding college students in dormitories and Armed Forces personnel in barracks) are classified as being above or below the poverty level, using the poverty index adopted by a Federal Interagency Committee in 1969. This index takes into account such factors as family size, number of children, and farm-nonfarm residence, as well as the amount of money income. The poverty level is based on an economy food plan designed by the Department of Agriculture for emergency or temporary use when funds are low. The definition assumes that a family is classified as poor if its total money income amounts to less than approximately three times the cost of the economy food plan. These cutoff levels are updated every year to reflect changes in the Consumer Price Index.
In 1970, percent below poverty level is calculated as the proportion of the total universe which reports income below the poverty level: for example, below poverty level families as a percent of all families.

Two or more persons living in same household who are related by blood, marriage, or adoption. (No families are recognized in group quarters. ) All persons living in a household related to each other are regarded as one family. For instance, a son of the head and his wife living in the household are treated as part of the heads family.

The number of families does not necessarily equal the number of households, since not all households include families. Families are classified in the complete-count basic records by family size or number of persons in a family from 2 persons to 35 persons. Average number of persons per family is calculated.

Married couple with or without own children, or one parent with one or more own children (parent-child group), living in a housing unit and related to the household head, but excluding the head (for example, a son, his wife and children, living with the household head). Since subfamily members are counted as part of the heads (primary) family, too, the number of subfamilies is not included in the count of families per seer in any tabulations for families. Census basic records include categories of sub-families by family type.

In 1960, a family in a household whose head was not related to the household head. In 1970, secondary families are not recognized (since there are so few); persons formerly classed as secondary family members are classed as secondary individuals.